PROJECT SUMMARY/ABSTRACT The skeleton is highly sensitive to mechanical loading and unloading. Skeletal unloading increases bone marrow adiposity and accelerates the loss of bone quantity and quality. Conversely, skeletal loading decreases bone marrow adiposity and increases skeletal integrity. While this beneficial effect of skeletal loading is well- known, the specific cell types and the molecular mechanisms contributing to these effects are unclear. Preliminary data show that global deletion of the auxiliary ?2?1 voltage-sensitive calcium channel (VSCC) subunit results in osteopenia, impairing skeletal development, decreasing bone mass and bone formation, and increasing adiposity. As several cell types regulate bone formation and responses to skeletal loading, we hypothesize that the impaired activity of either osteocytes and/or bone marrow mesenchymal stem cells (MSCs) contribute to the decline in bone formation seen in global ?2?1 knockout mice. Thus, the proposed studies will examine the cell-specific mechanisms by which the auxiliary ?2?1 subunit regulates skeletal development and anabolic responses to loading. Using transgenic mouse models, ?2?1 will be selectively deleted in osteocytes and the limb-bud mesenchyme. Additionally, treatment with the neuropathic pain drug gabapentin, which binds ?2?1 will determine SA1) If deletion of ?2?1 in osteocytes or chronic GBP treatment impairs basal or load-induced bone formation with resultant loss in bone quality, and SA2) If deletion of ?2?1 in mesenchymal progenitors or chronic GBP treatment influences skeletal development, bone formation, and bone marrow adipogenesis. Additionally, Dr. Wright will conduct complementary RNA sequencing analyses and in vitro work to support in vivo results. Dr. Wright is a nutritional musculoskeletal scientist with considerable expertise in clinical dietary interventions, analytical analyses, and animal research whose long- term career goal is to become a NIH-funded, tenured faculty member who conducts innovative, translational musculoskeletal research. Dr. Wright is currently obtaining advanced training in molecular biology and animal modeling to complement his clinical background and develop the technical expertise needed to accomplish his career goals. Dr. Wright and his mentoring committee have developed a comprehensive training plan and research proposal that will build upon his previous research experience, and further expand his skills in basic biological research. Dr. Wright's primary training objectives include 1) Participating in professional development events; 2) Taking advanced didactic training courses; 3) Acquiring translational biomolecular research experience; 4) Learning new experimental techniques; and 5) Enhancing writing abilities. Collectively, these activities will expand Dr. Wright's knowledge and research abilities; providing him the crucial expertise necessary for a productive career. The F32 award will greatly aid in Dr. Wright's career development, providing the financial assistance and the protected time necessary to achieve these research and training objectives.